Afghan President Hamid Karzai on Friday accused the United States of failing to cooperate in the probe of a massacre of 16 Afghan villagers, allegedly by a U.S. soldier.

President Karzai met with tribal elders and family members of those killed in Sunday's shooting spree in Kandahar province's Panjwai district. Speaking to reporters afterwards, he complained that the U.S. military was not sharing information with Afghan officials investigating the killings.

"The army chief has just reported that the Afghan investigation team did not receive the cooperation that they expected from the United States," said Karzai. "Therefore, these are all questions that we'll be raising, and raising very loudly, and raising very clearly.”

The Pentagon's decision to try the accused soldier under U.S. military law has angered many in the country. The soldier was flown out of Afghanistan to Kuwait late Wednesday, and officials later said the soldier was being flown Friday to a maximum security prison at a U.S. military base in the state of Kansas.

The soldier's civilian lawyer said his client was likely suffering from stress after witnessing one of his fellow soldiers sustain a grave injury, and was unhappy about being assigned a fourth tour of duty in a war zone.

Karzai lashed out about civilian casualties, saying they had been happening "for too long" and that he was at "the end of the rope." He said "this behavior can no longer be tolerated."

The Afghan leader also publicly reiterated claims by some villagers in the Panjwai district that more than one U.S. soldier was involved in the attack, in which children were among those killed.

"They believe it's not possible for one person to do that," said Karzai. "In his family, in four rooms, people were killed, women and children were killed, and they were all brought together in one room and then put on fire. That, one man cannot do.”

On Thursday, President Karzai met with U.S. Defense Secretary Leon Panetta in Kabul and demanded that NATO forces pull back from Afghan villages and relocate to their bases in the wake of the shooting spree.

Also Friday, U.S. military officials said a top U.S. commander in southern Afghanistan was in the path of an attack that coincided with Panetta's arrival in Afghanistan on Wednesday. They had initially downplayed the incident.